docs: def set_annotation(self):
          """Appends the context's ``pending_symbol`` to its ``annotations`` sequence."""
          assert self.pending_symbol is not None
          assert not self.value
          annotations = (_as_symbol(self.pending_symbol, is_symbol_value=False),)  # pending_symbol becomes an annotation
          self.annotations = annotations if not self.annotations else self.annotations + annotations
          self.ion_type = None
          self.pending_symbol = None  # reset pending symbol
          self.quoted_text = False
          self.line_comment = False
          self.is_self_delimiting = False
          return self